Pluto, planet, discovered 1930 and named after Πλουτων (ploutōn), the Greek god of the underworld

History & Etymology

First prepared in 1940-41 Glenn T. Seaborg (1912-1999), Edwin M. McMillan, Joseph W. Kennedy, and Arthur C. Wahl at the Berkeley Laboraty of the University of California by bombardement of Uranium with deuterons.

The second element following Uranium is named after the second planet after Uranus: Pluto, discovered in 1930 and named after Πλουτων [ploutōn], the Greek god of the underworld. About the naming, Glenn T. Seaborg said in 1996:

"In that first report [March 21, 1942], we decided to name the element Plutonium, just like Uranium is named after Uranus, Neptunium by McMillan and Abelson after Neptune, we decided to name it Plutonium. We should have named it plutium, but we liked Plutonium better. It just sounded better. And the symbol obviously should have been Pl, but we liked Pu better so we gave it the symbol Pu." (on-line).

The report was held secret until after the World War II when it was published in the Journal of the American Chemical Society in 1948. This is where the names Plutonium and Neptunium were first revealed.

In his autobiography, Seaborg says more about the naming of Plutonium (note) :

It was so difficult to make, from such rare materials, that we thought it would be the heaviest element ever formed. So we considered names like extremium and ultimium. Fortunately, we were spared the inevitable embarrassment that one courts when proclaiming a discovery to be the ultimate in any field by deciding to follow the nomenclatural precedents of the two prior elements.
A new planet had been discovered in 1781 and, like the rest of the planets, named for a Greek or Roman deity-Uranus. A scientist who discovered a heavy new element eight years later named it after the planet: uranium. A scientist who discovered a heavy new element eight years later named it after the planet: uranium. The planet Neptune was discovered in 1846, so Ed McMillan followed this precedent and named element 93 neptunium. Conveniently for us, the final planet, Pluto, had been discovered in 1930. We briefly considered the form plutium, but plutonium seemed more euphonious. Each element has a one- or two-letter abbreviation. Following the standard rules, this symbol should be Pl, but we chose Pu instead. We thought our little joke might come under criticism, but it was hardly noticed.

False transuranic elements (#93-97)

Element #94 has got in 1934-38 the preliminary name Eka-Osmium by Otto Hahn, Lise Meitner and Fritz Strassmann in Germany, who thought they had found traces of several transuranium elements. In December of 1938, Hahn and Strassman found out that these radioactivities were not due to transuranium elements but were due to fission products. According to the Periodic Table of that time, without the Actinide series, element #94 is below Osmium (#76). According to the present Table, Eka-Osmium would be #108.

Esperium, Hesperium

In 1934, Enrico Fermi (1901-1954) and his co-workers Amaldi, D'Agostino, Segrè, and Rasetti, after having bombarded Uranium with neutrons, believed to have synthesized the first transuranium elements. These were named Ausonium (#93) and Hesperium/Esperium (#94). See further at Neptunium.

Pluto and Plutonium

Pluto, formal designation 134340 Pluto, is the second-largest known dwarf planet in the Solar System (after Eris) and the tenth-largest body observed directly orbiting the Sun. Classified as a planet from its 1930 discovery, in 2006 the International Astronomical Union (IAU) declared it a dwarf planet instead; Pluto is now considered the largest member of a distinct population called the Kuiper belt.
Pluto was discovered on February 18, 1930, by Clyde W. Tombaugh, at Lowell Observatory, after nearly a year of searching on photographic plates taken on January 23 and January 29 of that year. The discovery made headlines across the globe. The Lowell Observatory, who had the right to name the new object, received over 1000 suggestions from all over the world, ranging from "Atlas" to "Zymal". Tombaugh urged Slipher to suggest a name for the new object quickly before someone else did. Constance Lowell proposed Zeus, then Lowell, and finally her own first name. These suggestions were disregarded. The name "Pluto" was proposed by Venetia Burney (later Venetia Phair), an eleven-year-old schoolgirl in Oxford, England. Venetia was interested in classical mythology as well as astronomy, and considered the name, one of the alternate names of Hades, the Greek god of the Underworld, appropriate for such a presumably dark and cold world. She suggested it in a conversation with her grandfather Falconer Madan, a former librarian of Oxford University's Bodleian Library. Madan passed the name to Professor Herbert Hall Turner, who then cabled it to colleagues in America. The object was officially named on March 24, 1930. The name was announced on May 1, 1930. Upon the announcement, Madan gave Venetia five pounds as a reward
(note).

The name was soon embraced by wider culture. The Disney character Pluto, introduced in 1930, was named in the object's honour. In 1941, Glenn T. Seaborg named the newly created element plutonium after Pluto, in keeping with the tradition of naming elements after newly discovered planets, such as uranium, which was named after Uranus, and neptunium which was named after Neptune

Pluto was god of the underworld and its riches. The name is the Latinized form of Greek Πλούτων (Ploutōn), another name by which Hades was known in Greek mythology, possibly from the Greek word for wealth, πλοῦτος (ploutos). It is debatable whether in the Roman pantheon he was considered a son of Saturn, as Hades was of Cronus. If so, he would have been one of the children devoured by Saturn, along with Neptune. Jupiter was saved and hidden from Saturn by Rhea. Together, they represented earth, water, and air (not as elements, but as environments). After Saturn's defeat, the three brothers took control of the world, and divided it into three separate parts for each brother to rule. Jupiter took control of the skies, Neptune of the seas, and Pluto ruled the underworld (Tartarus or Hades)
(note).